1. Field of the Invention
The present invention relates to control circuits, and particularly to a charger control circuit with automatic terminal polarity selection.
2. Description of Related Art
The battery packs for portable power tools, outdoor tools and certain kitchen and domestic appliances may include rechargeable batteries, such as lithium, nickel cadmium, nickel metal hydride and lead-acid batteries, so that they can be recharged rather than replaced. Thereby a substantial cost saving is achieved.
Rechargeable batteries are charged by a DC battery charger. Generally, battery chargers include an alternating current (AC) to direct current (DC) (or DC to DC) adapter containing an AC to DC (or DC to DC) converter for generating a substantially constant current to charge the battery to a nominal battery voltage. The chargers also include an output port with a positive terminal and a negative terminal for connecting the charger to the depleted battery. When connecting the charger to the battery, the positive terminal of the output port must be connected to the positive terminal of the battery, and the negative terminal of the output port must be connected to the negative terminal of the battery or to ground so that the direct current is supplied to the positive terminal of the battery.
If the positive and negative terminals of the output port of the battery charger are reversely connected to the battery terminals, the battery charger will supply the direct current to the negative terminal of the battery. This situation can result in overheating of the battery charger, excess arcing between the connection cables and the terminals of the battery, and, in extreme cases, battery explosions.
What is needed, therefore, is a charger control circuit which can solve above problem.